[blue sky]

4HU is Salisbury's identification for the gear size. It is equivalent to the Dana 44 whom Salisbury bought the right to use their patent. That designation incorporates both solid axles and IRS units. If it is an IRS unit from a Jag, it will be the common design use in most component cars out there. Original Cobras used a 4HU unit with a case of a different design with respect to how it was attached to the chassis. The 66 case will be the first IRS design with one piece stub/flange axles as opposed to the earlier design where the flange bolted to the stub axle. Log onto XK's Unlimited web page and go through their parts catalog and you can see the differences in the diffs. Hope this helps.